1. Field of the Invention
The present invention relates to a semiconductor manufacturing method. More particularly, the present invention relates to methods for forming a structured tungsten layer and forming a semiconductor device using the same.
2. Description of the Related Art
In a semiconductor device, plugs and interconnections are typically formed of low resistance material, e.g., metals such as aluminum, copper or tungsten. Tungsten may exhibit good step coverage and, accordingly, the use of tungsten has increased as semiconductor devices have become more highly integrated and critical dimensions have been reduced. The use of tungsten also has other advantages as a result of its various other properties, e.g., a relatively high melting point of more than 3400° C. and a strong resistance to electromigration.
In a semiconductor device, a tungsten layer is typically formed using a chemical vapor deposition (CVD) method or an atomic layer deposition (ALD) method. Forming a tungsten layer for interconnections or contact plugs by ALD may require significant process time, which may result in reduced manufacturing throughput. Therefore, the CVD method may be preferred, because this method typically can be carried out in less time.
However, the CVD method typically exhibits poorer step coverage than the ALD method. In order to accommodate the various deficiencies in these methods, tungsten layers have been formed using ALD to provide nucleation, and then forming a bulk layer of tungsten to a desired thickness using CVD. However, the resulting tungsten layer may have an upper surface that is very rough and nonuniform, as illustrated in FIG. 1.
If a tungsten layer having a nonuniform upper surface is formed using this conventional process, various defects may result. For example, where subsequent processes are performed, particles may remain at recessed regions of the rough upper surface, which may give rise to various problems. In addition, if another interconnection or conductive plug is formed during a subsequent process on the tungsten layer produced by this conventional method, voids may be formed on the upper surface that can cause problems, e.g., contact failures, a rise in interfacial resistance, etc. Further, the problems caused by the rough upper surface may become more serious as semiconductor devices become more highly integrated.